This invention relates to underreaming and chambering tools and more particularly to mechanisms in such tools for controlling the position of cutter arms.
Rotary drills are commonly used for earth boring operations. Such drills are employed in oil and gas wells as well as in mining operations. Often it is desired to enlarge the diameter of a hole drilled at some point a substantial distance below the surface. In oil and gas wells this is commonly referred to as underreaming, whereas in mining it is commonly referred to as chambering. For ease of explanation, both operations are generally referred to herein as underreaming.
To effect underreaming operations a variety of underreamers, hole openers, and the like have been devised. With some devices the underreamer can only be installed on the drill string when underreaming operations are taking place. This requires removal of the drill string each time a change is made from straight drilling to underreaming or vice versa.
Other devices employ various controllable cutter actuators to move underreaming cutters into or out of underreaming position while a drill is connected below the underreamer for drilling purposes. Some such devices use fluid pressure, for example, due to recirculating drilling mud or like to actuate a cutter into an extended cutting or underreaming position. In other known underreaming devices, mechanical adjustment of the drill string connected to the underreamer and fluid or pneumatic pressure applied through the drill string is used to move cutters to the underreaming position. One such device is disclosed in U.S. Pat. No. 3,817,339. In other devices purely mechanical control is employed. Known controllable cutter underreaming tools generally suffer from a variety of disadvantages. For example, some underreamers require a sequence of longitudinal and/or angular movement on the drill string, connected to the underreamer, in combination with application and/or removal of fluid or pneumatic pressure, to control and actuate the cutters. It will be appreciated that the sequencing has to be done at the drilling rig at the top of the hole being drilled with the underreamer at some remote location down hole. Thus the correct sequencing of up and down movement and rotational movement and the air pressure or fluid pressure needs to be applied through the drill string to the underreamer at the surface of the hole. As a result it is quite easy to make a mistake in the sequencing and as a result cause the cutter arms to be extended and thereby underream in an area where underreaming is not required and even not desired, or fail to make the desired underreaming cut.
Additionally it has been found with some underreamers that when a drill is connected to the end of an underreamer and it is desired to drill a hole without underreaming, the cutter arms on the underreamer may inadvertently fly out under force created by the rotating underreamer and cutter arms. As a result, underreaming may occur in areas of the hole where it is undesirable.
It should be noted that underreaming at and only at the correct position in the hole is of extreme importance. For example, in mining operations it is desired to underream in a limited area towards the bottom of the hole so that when explosive material is positioned in the hole and detonated, all of the energy from the explosion is concentrated in the limited area. Therefore, should underreaming extend too high in the hole, a substantial reduction in efficiency will be found.
Additionally in pneumatically controlled devices, it has been found that leakage in the pneumatic system can cause malfunctioning of the underreamer and errors in the underreaming process.
It has also been found that many prior art devices involve complicated spring loaded or other actuating mechanisms which are costly and/or of questionable reliability.